(a) Field of the Invention
The present invention relates to an organic electroluminescent device having an excellent luminescence property such as high luminance efficiency.
(b) Description of the Related Art
An organic electroluminescent device (which will hereinafter be called “organic EL device”) is a light-emitting device which makes use of the principle that when an electric field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode
After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, Vol. 51, 913 (1987) and the like), studies on an organic EL device have been briskly carried out. Tang et al reported an organic EL device using tris(8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; blocking of electrons injected from a cathode, which increase the efficiency of exciton production from charge recombination; and confine the excitons into the light-emitting layer. A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices.
As a hole transporting material, triphenylamine derivatives and aromatic diamine derivatives such as 4,4′,4″-tris(3-methylphenylphenylamino)-triphenylamine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine which are star burst type compounds are well known (for example, JP-A-8(1996)-20771, JP-A-8(1996)-40995, JP-A-8(1996)-40997, JP-A-8(1996)-53897, and JP-A-8(1996)-87122).
As an electron transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
Chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like are known as light emitting materials. Since various color light in a visible region from blue to red are obtained from these light-emitting materials, there is increased expectation for industrialization of a full color organic EL device (refer to, e.g., JP-A-8(1996)-23965, JP-A-7(1995)-138561, and JP-A-3(1991)-200889).
Although the various organic EL devices with high brightness and long lifetime have been reported, these properties are not enough. The present inventors described the organic EL devices with the high brightness using the specified perylene compound or the specified benzoperylene compound in JP-A-11(1999)-144869 and JP-A-11(1999)-185961.
However, sufficient performances are not obtained for some of the perylene compounds and the benzoperylene compounds because of the aggregation of compound molecules Other compounds used in organic EL devices also form molecular aggregation which causes concentration quenching in the case of a mixture with high concentration and the solid containing the compounds singly, and the concentration quenching reduced brightness of the devices in many cases.